As a means for mounting a semiconductor device in a liquid crystal display unit, a so-called chip-on-glass (to be referred to as COG hereinafter) method in which a semiconductor device is mounted in a substrate consisting of glass will be described with reference to FIGS. 4 and 5. FIG. 4 is a sectional view showing a projecting electrode provided to a semiconductor device. FIG. 5 is a sectional view showing a mounting structure in which the semiconductor device and a substrate are connected to each other by using the COG method.
As shown in FIG. 4, a protective film 13 is formed such that a connection pad 12 formed on the element formation surface of a semiconductor device 11 and consisting of aluminum is exposed. A common electrode film 14 is formed on the connection pad 12 to prevent adhesion to the connection pad 12 or diffusion. A projecting electrode 15 is formed using a metal such as copper or gold (Au) by a plating method or a vacuum evaporation method. The projecting electrode 15 is also formed on a semiconductor element formation region to improve the mounting density.
A method of connecting the semiconductor device 11 having the projecting electrode 15 formed thereon to a connection electrode 17 arranged on a substrate 16 will be described below with reference to FIG. 5.
As shown in FIG. 5, a conductive adhesive 18 obtained by mixing conductive particles 19 in an epoxy adhesive is coated at the distal end portion of the projecting electrode 15 of the semiconductor device 11 by a dip method or a printing method.
Thereafter, using a binocular microscope, alignment between the semiconductor device 11 and the substrate 16 is performed, thereby connecting the connection electrode 17 formed on the substrate 16 consisting of glass to the projecting electrode 15.
The connection electrode 17 is constituted by a transparent conductive film of indium tin oxide (to be referred to as ITO hereinafter) or the like.
A heat treatment is performed to harden the conductive adhesive 18 and evaporate the solvent of the conductive adhesive 18.
With this process, the conductive particles 19 and the projecting electrode 15, the conductive particles 19 and the adhesive electrode 17, and the conductive particles 19 are rendered conductive with each other, thereby obtaining satisfactory electrical connection.
In addition, by a tensile stress between the semiconductor device 11 and the substrate 16, which is generated by volume reduction of the conductive adhesive 18, an adhesion for stabilizing the connection is generated, and the electrical connection properties are improved.
Thereafter, a sealing resin 20 consisting of an organic material such as an epoxy material is poured into the gap between the semiconductor device 11 and the substrate 16, and a heat treatment is performed to harden the sealing resin 20.
A problem to be solved by the present invention will be described on the basis of the accompanying drawings. FIG. 1 is a plan view showing the connection electrodes 17 on the glass substrate and the conductive adhesives 18 after hardening when viewed from the upper side.
To increase the display density of a liquid crystal display unit, the pitch between the connection electrodes 17 in the right-and-left direction in FIG. 1 must be reduced. Conventionally, the pitch between the connection electrodes 17 is about 300 .mu.m. However, the use of a pitch of 150 .mu.m or 100 .mu.m has been examined.
In accordance with a reduction in the pitch between the connection electrodes 17, the diameter of the projecting electrode of the semiconductor device is reduced, and the size of the conductive adhesive 18 formed on the projecting electrode is reduced accordingly.
However, when the conductive adhesive is to be formed on the projecting electrode by the printing method as described above, because of the influence of variations in height of the projecting electrode or variations in flatness of the semiconductor device or a printing apparatus, the formation amount of the conductive adhesive is locally increased. In this case, the size of the conductive adhesive is undesirably increased at some portions.
Therefore, when high-density mounting is to be performed, a short circuit between a conductive adhesive and another conductive adhesive, which is indicated by an arrow 23 in FIG. 1, or a short circuit between a conductive adhesive and a connection electrode, which is indicated by an arrow 24 in FIG. 1, is generated. This causes a decrease in connection yield and makes it difficult to increase the density of the connection electrodes 17.
To solve this problem, the present invention has as its object to provide a semiconductor device having a connection structure for preventing a short circuit between connection electrodes, which is caused by a conductive adhesive or a solder, even in high-density connection with a connection pitch of 150 .mu.m or less, thereby obtaining a high connection yield.